Duality in cosmological perturbation theory

TL;DR

This paper demonstrates a duality symmetry in cosmological perturbation equations, introduces a duality-invariant approximation for super-horizon perturbations, and discusses implications for particle production during high curvature epochs.

Contribution

It reveals a duality invariance in cosmological perturbation theory and proposes a new approximation valid during high curvature periods.

Findings

Perturbation equations are invariant under duality transformations.

A duality-invariant approximation for super-horizon perturbations is introduced.

Duality implies bounds on particle production in the early universe.

Abstract

Cosmological perturbation equations derived from low-energy effective actions are shown to be invariant under a duality transformation reminiscent of electric-magnetic, strong-weak coupling, S-duality. A manifestly duality-invariant approximation for perturbations far outside the horizon is introduced, and it is argued to be useful even during a high curvature epoch. Duality manifests itself through a remnant symmetry acting on the classical moduli of cosmological models, and implying lower bounds on the number and energy density of produced particles.